The goals of the proposed work are 1) to examine the role of cholera-like, heat-labile toxin of E. coli, and possibly other fecal bacteria in sporadic infantile diarrhea and 2) to examine the relationship between the acquisition of toxigenic fecal bacteria and development of immune response to toxin. Work is proceeding to achieve these goals by weekly fecal sampling of a cohort of normal babies--the longitudinal group--who were enrolled at birth and are presently being followed, the intention being to follow each baby up to the age of two years, to compare episodes of diarrhea with acquisition of toxigenic bacteria. Cord sera and serum specimens collected at six monthly intervals will be stored for simultaneous determinations of toxin-specific immunoglobulins at the conclusion of the study. Additional serum samples are collected in conjunction with diarrhea episodes. Children who are being treated for diarrhea by the clinical services of the hospital are beeng observed with fecal samples and acute and convalescent sera to compare etiologies of diarrhea in them with etiologies of diarrhea among the longitudinal group.